Solid inkjet imaging systems generally use an electronic form of an image to generate firing signals that operate inkjets within printheads to eject ink melted from a solid ink stick or pellet onto an image receiving surface to reproduce the electronic image. In some solid inkjet imaging systems, the ink is ejected directly onto a media sheet, while in other solid inkjet imaging systems, the ink is ejected onto the surface of an intermediate imaging member and the ink image is transferred to a media sheet passed through a nip formed between the intermediate imaging member and a transfer roller. The heat and pressure in the nip help transfer the ink image from the intermediate imaging member to the media sheet, which is transported from the system and deposited in a paper tray.
In solid ink imaging systems having intermediate imaging members, ink is loaded into the system in a solid form, either as pellets or as ink sticks, and transported through a feed chute by a feed mechanism for delivery to a melting device. The melting device heats the solid ink to a temperature at which the solid ink melts and the melted ink is delivered to a printhead for jetting onto an intermediate imaging member. In the printhead, the liquid ink is typically maintained at a temperature that enables the ink to be ejected by the printing elements in the printhead, but that preserves sufficient tackiness for the ink to adhere to the intermediate imaging member. In some cases, however, the tackiness of the liquid ink may cause a portion of the ink to remain on the intermediate imaging member after the image is transferred onto the media sheet and the residual ink may degrade subsequent ink images formed on the intermediate imaging member.
To address the accumulation of ink on an intermediate imaging member, which may be in the form of a drum, solid ink imaging systems may be provided with a drum maintenance unit (DMU). In solid ink imaging systems, the DMU is configured to 1) lubricate the image receiving surface of the intermediate imaging member with a very thin, uniform layer of release agent before each print cycle, and 2) remove and store any excess release agent, ink and debris from the surface of the intermediate imaging member after each print cycle. During each print cycle, the release agent deposited on the intermediate imaging member may be controlled with a metering blade. The metering blade is designed to distribute release agent and remove excess release agent from the intermediate imaging member so the release agent does not adulterate the media sheet in the nip.
Release agent is removed from the DMU each time a page is printed. A DMU includes a limited amount of release agent, and the DMU must be replaced when the release agent is depleted. Therefore, applying only the amount of release agent necessary for efficient and effective transfer of an ink image to a printed media sheet without adversely affecting image quality on the sheet is desirable. If the release agent transferred to a media sheet falls below a predetermined threshold, however, print defects and media transport issues may occur. Applying the minimal effective amount of release agent is also affected by metering blade wear. Because metering blades wear with use over time, an excessive amount of release agent or an uneven layer of release agent may be applied to the intermediate imaging drum. An incorrect or inconsistent amount of release agent applied to the surface of the intermediate imaging drum may result in some of the solid ink adhering to the imaging drum or excess release agent being transferred to the media, which also causes print defects. Thus, improved and consistent metering of release agent in a solid ink printer is desirable.